The invention pertains to the control of light sources, and particularly to light source excitation at various temperatures. More particularly, the invention pertains to broadband source start-up at nearly any temperature range for a fiber optic gyroscope.
Light sources may be maintained at a certain temperature by thermoelectric coolers, heaters or other temperature sustaining devices. For instance, a heated light source must achieve operational status relatively fast, such as within about 100 microseconds. However, the heater associated with the light source has a time constant of about one minute. This means that when the light source is turned on before the heater reaches its steady state temperature, the light source can be damaged. If the light source is not damaged because of turn-on before the correct temperature is achieved, then the spectrum of the source may become significantly narrowed such that the gyroscope, which the light source is a part of, will have large rotation rate detection errors.
The current and the power of the light source are kept at appropriate levels with an adjustable current source and a system processor (CPU) which is used in the loop with a look-up table. The table provides a light source input current setting as a function of temperature of the light source environment. A heater may be situated proximate to the light source. Since the time constant of the heater is long, that is one to two minutes, relative to the needed sampling time, for example, one second updates, the loop can easily maintain the luminous power level desired out of the light source loop. During the turn-on transient, the wavelength of the source will vary with the source current and temperature. This means that the system needs some sort of characterization before achieving steady-state operation. After the steady state is reached, the current to the light source will be still controlled to provide a more refinely controlled wavelength of the source output. The compensated light source is useful in a fiber optic gyroscope since rotational detection error may occur as a result of an uncompensated light source.
U.S. Patent No. 5,410,515 by Bielas, et al., issued Apr. 25, 1995, and entitled xe2x80x9cRapid Turn-on Source for Fiber Optic Gyroscope,xe2x80x9d discloses a light source having wavelength compensation, which is hereby incorporated by reference. The light source is driven by a source, control circuit that generates a signal that is representative of the temperature of the light source. This signal compensates the wavelength of the source light relative to temperature. A scale factor for the fiber optic rotation sensor is also generated as a function of the compensation signal of the light source. A corrected scale factor signal may also be computer generated from an algorithm or from a look-up table. The referenced patent does not disclose a look-up table or the like for temperature compensation of the light source power or input current of a broadband light source over any startup temperature, for a fiber optic gyroscope, like the present invention.